The invention relates to a magnetoresistive (MR) head for reproducing information signals recorded on a magnetic recording medium by detecting changes in electrical resistance caused by the direction of magnetization of a magnetoresistive element being rotated on the basis of a magnetic field produced by recording magnetization of information signals recorded on a magnetic recording medium, such as a magnetic disc or magnetic tape.
There has hitherto been proposed a magneto-resistive head employing a magnetoresistive effect element formed of a magnetic alloy, such as permalloy, exhibiting a magneto resistive effect in which the electrical resistance is changed in accordance with the direction of spontaneous magnetization.
Such a magnetoresistive head is a magnetic flux responsive head that is now in widespread use. Since it is superior in response sensitivity to signals in the short wavelength range as contrasted to a magnetic head operating under electromagnetic induction, it makes possible reproduction of high-frequency signals. On the other hand, the length of the magnetic head can be reduced to contribute to reducing the width of the recording track formed on the recording medium. Besides, information signals can be reproduced with high sensitivity even with the magnetic recording medium run at a low velocity.
In general, a single-layer thin permalloy film is employed in a magnetoresistive element (MR element). The magneto-resistive head employing such single-layer thin permalloy film is subject to Barkhausen noise due to the movement of the magnetic wall. Since the MR element assumes a magnetic domain structure tending to hold the state of minimizing the sum of magnetostatic energies brought about by the energy of magnetic anisotropy or shape anisotropy for the entire layer, the magnetic wall is displaced if an external magnetic field is applied to the layer, thus producing the Barkhausen noise.
There is shown in JP Patent Kokai Publication A-1-251412 a magnetoresistive head designed to evade such Barkhausen noise. With the magnetoresistive head disclosed in this Publication, a pair of MR elements are laminated with a non-magnetic intermediate layer in-between to form a laminated MR element film, the front and rear ends of which are fitted with electrodes for passing the sense current. The laminated MR element film is sandwiched between a pair of shield magnetic members with an insulating film in-between, and a bias conductor is provided between one of the shield magnetic member and the laminated MR element film.
With the MR element of a stacked film structure, the easy axes of the upper and lower MR elements on either side of the non-magnetic intermediate layer become parallel to each other, while the directions of magnetization produced by passage of the sense current become opposite to each other, so that the MR elements cannot assume plural magnetic domains within the same plane, as a result of which the Barkhausen noise is prevented from being produced with the displacement of the magnetic wall.
If, with the MR elements of the laminated film structure, the magnetic gap is of a larger gap length, output stability is optimum because the magnetic equilibrium of the upper and lower MR elements is not disturbed by the shield magnetic member.
However, if the magnetic gap length is extremely narrow, such as 0.35 .mu.m or less, the shield magnetic member cannot be magnetically separated from the upper and lower MR elements, such that the magnetic equilibrium between the upper and lower MR elements becomes collapsed, as a result of which the output of the MR head becomes unstable.